The present invention relates to vial autosamplers of the type used for laboratory automation. More specifically, the present invention relates to sample mixing within the vial autosampler.
Vial autosamplers are used to automate laboratory analyses associated with gas chromatography, carbon measurement (total carbon and total organic carbon) as well as other types of analyses. Typically, a vial autosampler has a storage area adapted to hold a number of vials to be analyzed. A robotic system generally grasps one of the vials and transports it from the storage area to an analytical site. Once transported to the analytical site, the vial contents are sampled and the appropriate analysis is performed.
Autosamplers typically use separate sampling modules for extracting liquid and gas samples. One example of such an autosampler is described in U.S. Pat. No. 5,948,360 to Rao et al. and assigned to Tekmar Company of Cincinnati, Ohio. Liquid sampling typically involves extracting a known quantity of liquid from the vial that is presented to the sampling module of the autosampler, adding a standard to the sample, and transferring the sample to an analytical device. Under certain situations, the specimen must be diluted by a technician by injecting the specimen with a specified volume of methanol or a water-based solution prior to sampling. The extracted sample or methanol extract is then diluted with water prior to analysis by the analytical device.
Gas headspace extraction generally involves injecting the specimen with a solvent, such as water, agitating the specimen, and purging the specimen with a gas. Some autosamplers are adapted to perform static headspace extraction while others are adapted to perform dynamic headspace extraction. In static headspace extraction, the specimen is purged from above the specimen and the headspace is removed and transferred to the analytical device. In dynamic headspace extraction, the specimen is purged from underneath the specimen and the head space is removed and then transferred to the analytical instrument. Autosamplers that are capable of performing the above sample extraction include the Precept II and the 7000 HT autosamplers sold by Tekmar-Dohrmann, of Cincinnati, Ohio.
When sample agitation is desired, a stir member, such as a stir bar is generally provided within the vial. The stir member is designed to interact with magnetic fields. Then, a mixing mechanism subjects the stir member to varying magnetic fields. This is typically done by spinning a magnet either beside the vial, or under the vial. In these instances the magnetic field is simply varying, while remaining essentially stationary. This technique is limited in that the strength of magnetic coupling is not optimal. Thus, in samples where agitation may be a challenge, such as soil samples, the mixing mechanism may fail to generate rotation of the stir member, thus reducing the solvent's effects within the sample.
As sample analysis becomes more and more precise, quantifying concentration down into the parts-per-trillion, it becomes increasingly important to provide very effective sample agitation. A more effective mixing mechanism would indeed provide more effective analysis, while possibly reducing cycle times.